Polyphase stirring winding



'Aug. 14, 1956 1.. DREYFUS 2,759,035

POLYPHASE STIRRING WINDING Filed Aug. 10, 1954 7k [71 /a l I jnveh for Ludwzg Drgfus BY my Ht tomey;

iomm s'rinmNo Ludwig Dreyf Sweden, or to Alnshla Svenska Elektrlska Aktiebolaget, Vaeteru, Sweden, a Swedish corporation Application August 10, 1954, Serial No. man 2 Claims priority, application Great anon As 11, use 1 Chin!- (Cl. 13-2 The present invention relates to an improvement in stirring windings for melting furnaces or hot metal mixers.

In hitherto known stationary stirring windings for arc furnaces the winding is fed by symmetrical two-phase current with the result that the phase position of the A. C. currents changes from one current zone to the following w zone with 90 displacement. Since there are five current zones, 1, 2, 3, 4, (having respectively m, m, m, m and n5 conductors), the phase position for the two outermost zones 1 and 5 is the same. Due to the fact that the winding is mounted symmetrically with respect to the middle with the numbers of conductors in the five zones having therelationship,

and n:=ni, the two phases 1, 3, 5 and 2, 4, respectively, do not induce each other. These known stirring windings have been constructed as conventional coil windings, i. e. like the stator windings of polyphase synchronous generators or asyn-chronous motors. Thus the winding is embedded in a coarsely laminated slotted iron core and is fixed therein by laying the conductors into the slots and by staying the long double-curved ends of the coils by means of strong screw joints. 1

The above described stirring windings have the disadvantages that their manufacture is expensive, that a large stock of spare parts is required, since the coils are of unequal dimensions, and the winding requires a lot of space.

The stirring winding according to the present invention, by means of which the above drawbacks are all overcome, is characterised in that the winding consists of hollow coils, which slide on to coarsely laminated yokes without slots for retaining the conductors, and in that the winding of each yoke consists of five successive sections 1, 2, 3, 4, 5 having numbers of turns ni=ns, 'n:=m,

mEZnr and is fed symmetrically from two phases so that the current in one phase has 90' phase displacement with respect to the current in the other phase.

Such a stirring winding consists of five coils which can be wound in a simple winding machine. The coarsely laminated yoke may consist of two straight legs, which are joined together and positioned below the bottom of the furance.

Two embodiments of the invention will now be described by way of example with reference to the accompanying drawing, in which Figure 1 shows one form of the stirring winding arranged below the bottom of the furnace,

Figure la is a wiring diagram for-the coils of the stirring winding,

Figure 2 and 2a show modified forms of a part of the winding Figure 1,

Figure 3 is an end view of the winding and core parts shown at Figures 2 and 4,

Figure 4 is a view corresponding to Figure 3 but show- 2 ing a modified form of windings and cores arranged below a furnace bottom having staying girders.

Referring to Figures 1 3, the bottom of the furnace is designated by 10. The stirring winding, generally designated by 20, is a two-phase winding for a furnace having a curved bottom. The coarsely laminated iron yoke has its iaminations indicated by vertical lines in Figures 3 and'4 and consists of two straight legs 30, which are joined together at an angle of l80-e, where the centre 10 angle of the furnace bottom is 21:. Each leg supports coils having three current zones 1, 2, 3' and 3", 4, 5 respectively, wherein 3' and 3" constitute one current zone. The condition for symmetry is that the number of turns of the current zones ni=ns, m=m, but for the total number of turns of the middle zone ris(nr+ns) is permissible. The wiring diagram for the coils of the stirring winding is shown in Figure la. The coils 1, 3', 3" and 5 are fed from one phase while the coils 2 and 4 are g0 fed from the other phase, the directions of the currents being indicated by full line arrows and dotted line arrows, respectively, for t e corresponding phases. The lighest yoke is obtained ith ns (n1+ns). The coils of this configuration are all of equal radial dimensions so 25 that the keeping of a stock of spare parts is facilitated.

The coils are insulated from each other by means of intermediate pieces 80. The stirring windings may be protected by means of members of refractory material positioned between the winding and the bottom of the i0 furnace. Ventilation and cooling ducts 40 are arranged tween the yoke 30 and the coils 20. See Figures 2 and 4, thefiow of airbeing indicated by the arrows in Figure 2. Spacer bars are inserted between the coils and the yoke. The winding may also be constructed for 36 internal water cooling as indicated in Figure 2a.

Measures may be taken for minimising the reactive power of the winding. In contradistinction to the coil winding of the conventional type, in the new winding approximately the same flux per cm. length of conductor (0 emerges from its lower side and short sides. This fiux does not contribute to the stirring forces but increases the reactive power to the same amount as or somewhat above the amount occurring in coil windings of the known type. It is therefore suitable to make the casing 50, by means of which the winding has to be protected, of metal of low electric ohmic resistivity.- In this case, eddy.cur-

rents are generated in the casing, which eddy currents minimise the inelfective part of the magnetic fiux with the result'that the reactive power is reduced.

In the case of a furnace with a plane bottom the yoke may consist of two straight legs, such as the legs 30 of Figure 1, which legs are joined together in alignment with each other and suitably reinforced. The middle current zone would be divided into two equal halves.

Finally the invention permits the division of the stirring means along their width into two or more narrower stirring means of equal length and equal zone distribution, which further facilitates the keeping of a stock of spare parts. This construction also permits the introduction of one or more girders (preferably of non-magnetic material) which act as staying means for supporting the bottom of the furnace. This embodiment is shown in Figure 4. I The staying means are indicated by the numeral 60.

Although the new windings are described for use with melting furnaces, it lies in the scope of the invention to use them for hot metal mixers.

I claim as my invention:

1. A polyphase stirring winding system for stirring the metallic'charge in a container for molten metal, comprising hollow coils, at least one laminated non-slotted magnetic yoke arranged below the bottom of the container and within said coils, the winding system of the coils consisting of five successive sections 1, 2, 3, 4, 5, havmg numbers of turns n1=ns, m=m, nsEZm, and being supplied with a polyphase current for symmetrically feeding the said successive sections so that the current in the one phase has 90' phase displacement with respect to about a central plane at right angles to the longitudinal extension of the winding.

3. A polyphase stirring winding system of the type described, comprising five successive sections arranged end-to-end and with the middle section divided'into two equal halves disposed symmetrically about a central plane at right angles to the longitudinal extension of the winding, and a yoke consists of two equal legs joined together in alignment with each other to provide a reinforced junction.

4. A polyphase stirring winding system of the type described, comprising five successive sections placed below a curved bottom of a molten metal container having a center angle of 2-6:, and the middle section being divided into two equal halves disposed symmetrically about 4 a central plane at right angles to the longitudinal extension of the winding. and a yoke consists of two equal legs forming an angle of approximately ISO-a at their junction point to provide a reinforced junction.

6. A polyphase stirring winding system according to claim 1, comprising intermediate pieces whereby the coil: carrying current of different phases are insulated from each other and a space provided between the coils and the yoke for the purpose of cooling.

6. A polyphase stirring winding system according to claim 1, comprising metallic members of low ohmic resistivity covering at least a part of the lateral and lower sides of the coils for minimizing the ineffective part of the magnetic flux.

' tom of the container;

References Cited in the file of this patent UNITED STATES PATENTS Northrup Feb. 10, 1931 1,943,802 Northrup Jan. 16, 1934 

